As the minimum feature size achievable, in semiconductor manufacturing decreases, the capacitive coupling between adjacent devices becomes a significant impediment to achieving higher performance. Unfortunately there are only a limited number of potential solutions to this problem. As the minimum feature size decreases the number of devices potentially achievable, in a given area, increases with the inverse square of the feature size while the space between devices decreases linearly. As the density of devices is raised, the amount of interconnection metallurgy must also be raised, which has the effect of increasing undesirable capacitive interactions between circuits on the chip. Designers and process engineers have been looking for ways to counteract this wiring capacitance problem.
One approach has been to substitute lower dielectric constant materials with air gap insulator configurations between active devices. Such air gaps or air bridges have been employed to a limited degree for certain specialized applications. However, the use of air gap insulation introduces some other design challenges. For example environmental corrosion of exposed air structures are a concern. Additionally, heat must be removed from air bridge structures. Because continuing device size reductions require that the cross sections of the metal conductor lines also be reduced, the electrical resistance per unit length of the conductors is increased along with the generation of heat via resistive heating of the metallurgy. Replacement of the traditional aluminum and aluminum alloy conductors with more conductive copper is now underway but this only partially reduces the heating problem.
Although a specific problem of reducing heat generated by air bridge interconnect structures is described, a more general problem includes the inefficiencies of the current wide range of integrated circuit operating temperatures. Because current devices are designed to operate in large ranges of temperatures (for example −20 to 80 degrees C. is not uncommon) a number of design compromises must be made. Material characteristics such as conductivity, electromigration, etc. change over these wide ranges of temperatures, therefore circuit designers must assume that several extreme temperature conditions are possible, and the circuits must be designed to be very robust over these large temperature ranges.
What is needed is a method and device to provide improved cooling for integrated circuits. What is also needed is a method and device that provides good insulating characteristics to reduce undesirable capacitive interactions in integrated circuits. What is also needed is a method and device to improve design efficiency and operational efficiency in integrated circuits.